Active agents (or drugs) are most conventionally administered either orally or by injection. Unfortunately, many active agent are completely ineffective or have radically reduced efficacy when orally administered, since they either are not absorbed or are adversely affected before entering the bloodstream and thus do not possess the desired activity. On the other hand, the direct injection of the agent intravenously or subcutaneously, while assuring no modification of the agent during administration, is a difficult, inconvenient, painful and uncomfortable procedure that sometimes results in poor patient compliance.
Hence, in principle, transdermal delivery provides for a method of administering active agents that would otherwise need to be delivered via hypodermic injection or intravenous infusion. The word “transdermal”, as used herein, is generic term that refers to delivery of an active agent (e.g., a therapeutic agent, such as a drug or an immunologically active agent, such as a vaccine) through the skin to the local tissue or systemic circulatory system without substantial cutting or penetration of the skin, such as cutting with a surgical knife or piercing the skin with a hypodermic needle. Transdermal agent delivery includes delivery via passive diffusion as well as delivery based upon external energy sources, such as electricity (e.g., iontophoresis) and ultrasound (e.g., phonophoresis).
Passive transdermal agent delivery systems, which are more common, typically include a drug reservoir that contains a high concentration of an active agent. The reservoir is adapted to contact the skin, which enables the agent to diffuse through the skin and into the body tissues or bloodstream of a patient.
As is well known in the art, the transdermal drug flux is dependent upon the condition of the skin, the size and physical/chemical properties of the drug molecule, and the concentration gradient across the skin. Because of the low permeability of the skin to many drugs, transdermal delivery has had limited applications. This low permeability is attributed primarily to the stratum corneum, the outermost skin layer which consists of flat, dead cells filled with keratin fibers (i.e., keratinocytes) surrounded by lipid bilayers. This highly-ordered structure of the lipid bilayers confers a relatively impermeable character to the stratum corneum.
One common method of increasing the passive transdermal diffusional agent flux involves pre-treating the skin with, or co-delivering with the agent, a skin permeation enhancer. A permeation enhancer, when applied to a body surface through which the agent is delivered, enhances the flux of the agent therethrough. However, the efficacy of these methods in enhancing transdermal protein flux has been limited, at least for the larger proteins, due to their size.
There also have been many techniques and devices developed to mechanically penetrate or disrupt the outermost skin layers thereby creating pathways into the skin in order to enhance the amount of agent being transdermally delivered. Illustrative is the drug delivery device disclosed in U.S. Pat. No. 3,964,482.
Other systems and apparatus that employ tiny skin piercing elements to enhance transdermal agent delivery are disclosed in U.S. Pat. Nos. 5,879,326, 3,814,097, 5,250,023, 3,964,482, Reissue No. 25,637, and PCT Publication Nos. WO 96/37155, WO 96/37256, WO 96/17648, WO 97/03718, WO 98/11937, WO 98/00193, WO 97/48440, WO 97/48441, WO 97/48442, WO 98/00193, WO 99/64580, WO 98/28037, WO 98/29298, and WO 98/29365; all incorporated herein by reference in their entirety.
The disclosed systems and apparatus employ piercing elements of various shapes and sizes to pierce the outermost layer (i.e., the stratum corneum) of the skin. The piercing elements disclosed in these references generally extend perpendicularly from a thin, flat member, such as a pad or sheet. The piercing elements in some of these devices are extremely small, some having a microprojection length of only about 25-400 microns and a microprojection thickness of only about 5-50 microns. These tiny piercing/cutting elements make correspondingly small microslits/microcuts in the stratum corneum for enhancing transdermal agent delivery therethrough.
The disclosed systems further typically include a reservoir for holding the agent and also a delivery system to transfer the agent from the reservoir through the stratum corneum, such as by hollow tines of the device itself. One example of such a device is disclosed in WO 93/17754, which has a liquid agent reservoir. The reservoir must, however, be pressurized to force the liquid agent through the tiny tubular elements and into the skin. Disadvantages of such devices include the added complication and expense for adding a pressurizable liquid reservoir and complications due to the presence of a pressure-driven delivery system.
As disclosed in U.S. patent application Ser. No. 10/045,842, which is fully incorporated by reference herein, it is possible to have the active agent that is to be delivered coated on the microprojections instead of contained in a physical reservoir. This eliminates the necessity of a separate physical reservoir and developing an agent formulation or composition specifically for the reservoir.
As is well known in the art, osteoporosis is a bone disorder characterized by progressive bone loss that predisposes an individual to an increased risk of fracture, typically in the hip, spine and wrist. The progressive bone loss, which typically begins between the ages of 30 and 40, is mainly asymptomatic until a bone fracture occurs, leading to a high degree of patient morbidity and mortality. Eighty percent of those affected by osteoporosis are women and, based on recent studies, during the six years following the onset of menopause, women lose one third of their bone mass.
As is also well known in the art, parathyroid hormone (PTH) is a hormone secreted by the parathyroid gland that regulates the metabolism of calcium and phosphate in the body. PTH has stirred great interest in the treatment of osteoporosis for its ability to promote bone formation and, hence, dramatically reduced incidence of fractures. Large-scale clinical trials have shown that PTH effectively and safely reduces the percentage of vertebral and non-vertebral fractures in women with osteoporosis.
PTH-based agents have also stirred interest in the treatment of bone fractures (in both men and women) by virtue of their ability to accelerate bone healing.
To this end, various stabilized formulations of PTH-based agents have been developed that can be reconstituted for subcutaneous injection, which, as discussed below, is the conventional means of delivery. Illustrative are the formulations disclosed in U.S. Pat. No. 5,563,122 (“Stabilized Parathyroid Hormone Composition”) and U.S. Patent Application Pub. No. 2002/0107200 (“Stabilized Teriparatide Solutions”), which are incorporated by reference herein in their entirety.
A currently approved injectable PTH-based agent is FORTEO™ (an rDNA derived teriparatide injection), which contains recombinant human parathyroid hormone (1-34), (rhPTH (1-34)). FORTEO™ is typically prescribed for women with a history of osteoporotic fracture, who have multiple risk factors for fracture, or who have failed or are intolerant of previous osteoporosis therapy, based on a physician's assessment. In postmenopausal women with osteoporosis, FORTEO™ has been found to increase bone mineral density (BMD) and reduce the risk of vertebral and non-vertebral fractures.
FORTEO™ has also been found to increase bone mass in men with primary or hypogonadal osteoporosis who are at high risk for fracture. These include men with a history of osteoporotic fracture, or who have multiple risk factors for fracture, or who have failed or are intolerant to previous osteoporosis therapy. In men with primary or hypogonadal osteoporosis, FORTEO™ has similarly been found to increase BMD.
In addition to subcutaneous injection, other means of delivering PTH-based agents have also been investigated. For example, various pulmonary delivery (i.e., inhalation) methods are discussed in “Pulmonary Delivery of Drugs for Bone Disorders,” Advanced Drug Delivery Reviews, Vol. 42, Issue 3, pp. 239-248 (Aug. 31, 2000), Patton, “Bioavailability of Pulmonary Delivered Peptides and Proteins:—Interferon, Calcitonins and Parathyroid Hormones,” Journal of Controlled Release, Vol. 28, Issues 1-3, pp. 79-85 (January 1994), Patton, et al., “Impact of Formulation and Methods of Pulmonary Delivery on Absorption of Parathyroid Hormone (1-34) from Rat Lungs,” Journal of Pharmaceutical Sciences, Vol. 93, Issue 5, pp. 1241-1252 (May 2004), Codrons, et al., “Systemic Delivery of Parathyroid Hormone (1-34) Using Inhalation Dry Powders in Rats,” Journal of Pharmaceutical Sciences, Vol. 92, Issue 5, pp. 938-950 (May 2003) and Pfützner, A, et al., “Pilot Study with Technosphere/PTH(1-34)—A New Approach for Effective Pulmonary Delivery of Parathyroid Hormone (1-34)”, Horm. Metab. Res., Vol. 35(5), pp. 319-23.
Various methods of active transdermal delivery of PTH-based agents are also discussed in “The Effect of Electroporation on Eontophoretic Eransdermal Delivery of Calcium Regulating Hormones,” Journal of Controlled Release, Vol. 66, Issues 2-3, pp. 127-133 (May 15, 2000) and Chang, et al., “Prevention of Bone Loss in Ovariectomized Rats by Pulsatile Transdermal Iontophoretic Administration of Human PTH(1-34),” Journal of Pharmaceutical Sciences, Vol. 91, Issue 2, pp. 350-361 (February 2002).
Despite the efficacy of PTH in treating disorders such as osteoporosis, there are several drawbacks and disadvantages associated with the disclosed prior art methods of delivering PTH, particularly, via subcutaneous injection. A major drawback is that subcutaneous injection is a difficult and uncomfortable procedure, which often results in poor patient compliance.
Intracutaneous administration of agents, such as hGH, using microprojection systems has previously been documented to provide a pharmacokinetic profile of hGH similar to that observed following subcutaneous administration. See, e.g., Cormier, et al., U.S. Patent Application Pub. No. 2002/0128599, entitled “Transdermal Drug Delivery Devices Having Coated Microprotrusions”.
Continuous infusion of a PTH-based agent in vivo results in active bone resorption. It is therefore of critical importance that the PTH-based agent be administered in a pulsatile fashion. Based on the efficacy results from the once daily subcutaneous injection, any alternative route of PTH delivery should provide blood concentration of PTH no slower than that for subcutaneously injected PTH.
It would thus be desirable to provide an agent delivery system that facilitates minimally invasive administration of PTH-based agents. It would further be desirable to provide an agent delivery system that provides a pharmacokinetic profile of the PTH-based agent similar to that observed following subcutaneous administration.
It is therefore an object of the present invention to provide a transdermal agent delivery apparatus and method that provides intracutaneous delivery of a PTH-based agent to a patient.
It is another object of the invention to provide a transdermal agent delivery apparatus and method that provides a pharmacokinetic profile of the PTH-based agent similar to or faster than that observed following subcutaneous administration.
It is another object of the invention to provide a transdermal agent delivery apparatus and method that provides pharmacologically active blood concentration of a PTH-based agent for a period of up to eight hours.
It is another object of the invention to provide a PTH-based agent formulation for intracutaneous delivery to a patient.
It is another object of the present invention to provide a transdermal agent delivery apparatus and method that includes microprojections coated with a biocompatible coating that includes at least one biologically active agent, preferably, a PTH-based agent.